1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus for forming an image by a radioactive ray such as a visible light or an X-ray, and for example, to a photoelectric conversion apparatus adapted to be used for a photoelectric conversion apparatus of one-dimension or two-dimension such as a still camera or a radioactive-ray image pickup apparatus.
2. Description of the Related Art
In convention, as said to be a photograph, a silver-salt photograph which uses an optical camera and a silver-salt film has occupied the major portion of the photographs. Even though the semiconductor technologies have been developed and the photoelectric conversion apparatuses have been developed which are capable of taking pictures of the images of motion pictures such as a video cam corder by using a solid state image sensing device using a Si single crystal as represented by the CCD type sensor, the MOS type sensor, these images can not be better than the silver-salt photograph with respect to the number of pixels as well as to the S/N ratio, and thus it has been common to use the silver-salt photographs for taking the static images thereinto.
Recently, the demands for image processing by a computer, a retention by an electronic file, and an image transmission by electronic mail have increased, and it is desired to have an electronic image pickup apparatus which outputs as a digital signal of similar quality to the silver-salt photograph image. This can be equally applied to not only the general photographs but also the fields of medical service and non-destructive inspection.
In the field of medical service an X-ray photograph is known as the one that uses a silver-salt photograph technology. This is the one in which an X-ray radiated from an X-ray source is irradiated to the diseased part of a human body, and with the information of that transmission, for example, it judges whether or not there is a broken bone or a tumor, and has been used for the medical diagnoses for a long time. (This can be said to be one the non-destructive inspections). Usually, the X-ray transmitted through the diseased part is to be incident once on a wavelength conversion unit such as a fluorescent material, and is converted to a light of the sensitive wave region such as a visible light, and then is exposure on the silver-salt film. Although the silver-salt film has advantages such as the silver-salt film has a goood sensitivity, and also has a high quality of resolution, but it has problems such as taking too much time for a development, taking a lot of time and labor for a retention/a management, and not readily to transmitted to a remote area, and the like, and thus it is desired to have an electronic X-ray image pickup apparatus which outputs the digital signal not of similar quality to the silver-salt photograph image as described above.
However, there still remains some points which should be improved in order to electronically read the X-ray images or the images converted from the X-rays and to use them as data for the medical service and/or non-destructive testing.
That is, it is needed to consider the problems of noises which could be added to the data, when adopting the electronic data. By adopting the noises with the image data, there is the possibility of resulting damage to the the medical diagnoses and/or the diagnoses of the structures by the non-destructive inspections.
Further, not only for the problem of noise, but also for reducing an exposure quantity to the human body, much high sensitive photo-electric conversion apparatus is required.